Theoretical Solid State Physics

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Many-body physics with quantum impurities in ultracold atoms and beyond

Richard Schmidt , ITAMP Harvard and ETH Zürich

02.02.2018 at 09:00 

Understanding the role of interactions between an impurity and its environment is a paradigm problem of quantum many-body physics. A central concept for the description of such systems is the formation of quasiparticle excitations called polarons. Depending on the character of the environment and the form of interactions, different types of polarons are created. In this talk, I will review recent experimental and theoretical progress on studying the many-body physics of polarons in ultracold atomic systems [1], and discuss related polaronic phenomena encountered in two-dimensional semiconductors [2] and the study of rotating molecules in superfluid Helium [3]. In the second part of the talk I will focus on impurities interacting with bosonic quantum gases. Specifically, I will discuss progress on the theoretical description of Rydberg excitations coupled to Bose-Einstein condensates. In such systems the interaction between the Rydberg atom and the Bose gas is mediated by the Rydberg electron. This gives rise to a new polaronic dressing mechanisms, where instead of collective excitations, molecules of gigantic size dress the Rydberg impurity. We develop a functional determinant approach [4] to describe the dynamics of such Rydberg systems which incorporates atomic and many-body theory. Using this approach we predict the appearance of a superpolaronic state which has recently been observed in experiments [5,6].

[1] R. Schmidt, M. Knap, D. A. Ivanov, J.-S. You, M. Cetina, and E. Demler, Rep. Prog. Phys. 81, 024401 (2018).
[2] M. Sidler et al., Nature Physics 13, 255 (2017)
[3] R. Schmidt, and M. Lemeshko, Phys. Rev. Lett. 114, 203001 (2015);
[4] R. Schmidt, H. Sadeghpour, and E. Demler, Phys. Rev. Lett. 116, 105302 (2016).
[5] F. Camargo et al., arXiv:1706.03717 (2017).
[6] R. Schmidt et al., arXiv:1709.01838 (2017).

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